Source radiocarbon

Ramsey, C.B. and Hedges, R.E.M., Hybrid ion sources Radiocarbon measurement from microgram to milligram, Nucl. Instrum. Methods Phys. Res. Sect. B, 123, 539, 1997. 

Bronk Ramsey C, and Hedges REM. Hybrid ion sources Radiocarbon measurements form microgram to milligram. Nucl Instrum Methods Phys Res 1997 B 123 539—545. 

Hassan, A.A. and Ortner, D.J. 1977 Inclusions in bone material as a source of error in radiocarbon dating. Archaeometry 19 131-135. 

A mass of evidence seems to confirm that the mixing rate of radiocarbon in the atmosphere is rapid, and that with respect to its radiocarbon content the atmosphere can be considered as a homogeneous entirety. The contamination of samples with matter from an extraneous source can nevertheless invalidate this assumption. Two types of contamination can be differentiated physicochemical contamination and mechanical intrusion. There are two forms of physicochemical contamination. One is due to the dilution of the concentration of radiocarbon in the atmosphere by very old carbon, practically depleted of radiocarbon, released by the combustion of fossil fuel, such as coal and oil. The other is by the contamination with radiocarbon produced by nuclear bomb tests during the 1950s and later in the twentieth century. The uncertainties introduced by these forms of contamination complicate the interpretation of data obtained by the radiocarbon dating method and restrict its accuracy and the effective time range of dating. 

Besides being used in many applications involving historical problems, as in the examples shown above, radiocarbon has been successfully employed in the study of prehistory, where it represents the main source of time perspective. AMS in particular has helped in extending the possibility of 14C. For example, radiocarbon dating of single seeds, only possible by AMS, has contributed to the study of the beginnings of agriculture.[82]... 

The reasons will be clearer after Section 16.4, where AMS radiocarbon sample preparation procedures will be described. Now we would simply like to recall that in preparing graphite pellets for the sputtering source, after a physical chemical cleaning, samples to be dated are usually combusted to obtain C02, which is then converted to graphite by a further step. In this process, the main problem with small samples (a few tens of micrograms) is the possible introduction of contamination. 

I turn now to the expression for a radioactive isotope, for example, radiocarbon. If lambda is the decay constant, the rate of loss of radioactive atoms by decay will be lambda r m. For the sake of generality, suppose that there is a source that generates radiocarbon at a rate equal to qrc. The conservation equation becomes... 

For radiocarbon, the standard ratio s is provided by the preindustrial atmosphere, for which 8 = 0. Cosmic rays interacting with atmospheric nitrogen were the main source of preindustrial radiocarbon. In the steady state, this source drsource is just large enough to generate an atmospheric delta value equal to zero. The source appears in equation 9 for atmospheric radiocarbon. Its value, specified in subroutine SPECS, I adjust to yield a steady-state atmospheric delta value of 0. The source balances the decay of radiocarbon in the atmosphere and in all of the oceanic reservoirs. Because radiocarbon has an overall source and sink—unlike the phosphorus, total carbon, 13C, and alkalinity in this simulation—the steady-state values of radiocarbon do not depend on the initial values. 

Fossil fuel source terms appear not only in equation 1 for atmospheric carbon dioxide fuel/matmco2 but also in equations 6 and 9 for carbon isotopes in the atmosphere fuel/matmco2 defuel or drfuel. The 13C delta value for the fossil fuel source is defuel = — 25, and the radiocarbon value is drfuel = —1000, because fossil carbon is devoid of radiocarbon, rfs = 0, and del = — 1 1000. 

The results for 14C are plotted in Figure 6-3. Again, the response of the atmosphere is quite pronounced. The response of the shallow ocean is less marked, and the deep ocean shows no response at all on this time scale. Radiocarbon ratios are lower in the ocean than in the atmosphere because radioactive decay reduces the 14C ratio. The difference between the steady-state atmosphere and the steady-state values in the oceanic reservoirs is an indication of how much time has elapsed since these masses of water last equilibrated with the atmosphere. Measurements of radiocarbon are an important source of information on the circulation of the deep ocean, and the differences between 13C ratios in the different reservoirs have quite different causes The deep ocean is lighter than the surface ocean because... 

Our project to test a Tandem accelerator for multi-beam detection was then to modify the accelerator analyzing magnet such that the various beams could be dispersed and detected simultaneously, to design an injection system to appropriately process the different isotopic beams from the ion source for injection into the accelerator, and to construct an ion-source to allow us to routinely handle small samples. Our interests at present lie in radiocarbon and radioberyllium studies, and so we have designed this system to accommodate these isotopes. 

All of the above particulate investigations were based on mini-radiocarbon measurement techniques, with sample masses typically in the range of 5-10 mg-carbon. This constituted a major advantage, because it was practicable to select special samples (given region, source impact, sediment depth) and to further subject such samples to physical (size) or chemical separation before 14C measurement. This type of "serial selectivity" provides maximum information content about the samples and in fact it is essential when information is sought for the sources or atmospheric distributions of pure chemical species, such as methane or elemental carbon. 

Characterization of Their Sources by Low-Level Radiocarbon Counting and Pyrolysis/Gas Chromatography/Mass Spectrometry, Conference on Carbonaceous Particles in the Atmosphere, T. Novakov, ed., University of California, Berkeley, p. 36, 1978. 

Amino acid composition data and stable isotope ratios are being evaluated as sources of information to indicate the presence of non-indigenous organics in bone samples intended for radiocarbon analyses. The study is being conducted in the context of the planned 14C measurement of Pleistocene bone samples by high energy mass spectrometric methods. 

Table 2. Concordance of Suite of Radiocarbon Determinations on Bone Collagen and Associated Organics. Source Berger et aL [14] and Personal Communication.

Hassan, A. A., Ortner, D. J., Inclusions in Bone Material as A Source of Error in Radiocarbon Dating, Archaeometry, 1977 19, 131-135. 

Table 8.3 Comparison of radiocarbon AMS and AAR dates on Paleoindian skeletons, compiled from various sources listed in the text. 

Broecker, W.S., T.H. Peng, and T. Takahasi. 1980. A strategy for the use of bomb-produced radiocarbon as a tracer for the transport of fossil fuel CO2 into the deep-sea source regions. Earth and Planetary Science Letters 49 463-468. 

Our initial studies (25,26) determined the comparative fate of a radiocarbon-labeled preparation of the commonly occurring linear furanocoumarln, xanthotoxln (8-methoxypsoralen) in black swallowtail caterpillars and in fall armyworm (Spodoptera frugiperda J. E. Smith) larvae. Black swallowtail caterpillars are known not to be adversely affected by linear furanocoumarlns (22), while Spodoptera spp. avoid such plants as food sources... 

As renewable raw materials began to enter the marketplace, it was inevitable that claims to the level of renewable content in commercial offerings would become an issue of public debate. As previously pointed out in this article, some renewable raw materials have been common to the polyol chemistry for many decades, so claims to at least some renewable content are justified. Because the commercialization of different renewable polyol chemistries has created a highly competitive environment, some scientists in the field have promoted a method for the independent verification of the renewable sourced carbon in the final product [153]. ASTM International has published a concise and informative briefing paper on the method development for the determination of renewable carbon content in carbon-containing substances [154]. The method involves the analysis of content in the finished polyurethane products via radiocarbon dating [155]. The technique is fast and accurate, and has become commonly available by contract analysis through independent analytical laboratories [156]. 

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